Any metallic structure which is positioned in an offshore salt water environment, will, after a period of time, be subjected to progressive corrosion and deterioration of exposed metallic parts. One way to prevent or at least deter such corrosive action is through the use of coatings such as paints and anti-corrosion systems which are capable of counteracting the deleterious effects. It has been found desirable for example to provide submerged parts of the structure with a series of sacrificial anodes. Thus, rather than the structure's metallic parts deteriorating under the cathodic effects of corrosive action, the sacrificial anodes will be progressively eaten away.
This method of corrosion control is widely practiced by the petroleum industry. Offshore drilling and producing structures frequently utilize sacrificial anodes in their prevention systems.
To maintain a desired degree of protection for the structure, these sacrificial anodes must be replaced. Normally, structures are subjected to periodic inspections usually by divers who descend with the necessary instrumentation to both test and observe the degree of protection afforded by the many sacrificial anodes. In relatively shallow water, the use of divers is found to be practical and entails minimal expenses.
The present generation of offshore structures of the type contemplated is often made for use in water depths on the order of magnitude of 1,000 feet and greater. It can be appreciated therefore that for such a structure, the use of divers to periodically descend and check the anti-corrosion system can prove to be an expensive as well as a dangerous operation.
The prior art has dealt with the subject of cathodic protection and monitoring equipment therefor. U.S. Pat. No. 4,056,446, for example, teaches the use of an instrument package which is guidably raised and lowered through an offshore structure to gather the necessary data. This arrangement, however, embodies limitations which restrict its utility.
Toward simplifying the monitoring and inspection process for relatively tall or deep offshore structures, the present invention provides means whereby the cathodic protection system can be monitored without the use of divers and by a relatively simple apparatus incorporated into the structure. Said apparatus comprises primarily a package of monitoring instruments and ancillary equipment which is capable of being raised and lowered along a guide cable as well as being horizontally adjustable to more fully scan the structure.
It is therefore an object of the invention to provide a cathodic protection monitor system for a structure positioned in an offshore body of water.
A further object is to provide a corrosion prevention monitor system which is operated and controlled from a structure's deck whereby to avoid the use of divers.